1. Field of the Invention
The present invention relates to a method and an apparatus for measuring eccentricity of an aspherical lens having an aspherical surface on only one lens face. More particularly, the present invention relates to a method and an apparatus for measuring an angle between an optical axis of the aspherical lens having an aspherical surface on only one lens face and an axis of the aspherical surface.
2. Description of the Related Art
When an aspherical lens is constructed by a spherical surface on one lens face and an aspherical surface on another lens face, an optical axis of the aspherical lens is a connecting line between a center of curvature of the spherical surface and a center of curvature of a reference spherical surface as a base of the aspherical surface. An axis of the aspherical surface is a connecting line between the center of curvature of the reference spherical surface and an vertex of the aspherical surface. If the aspherical lens is manufactured as designed, the optical axis of the aspherical lens is completely in conformity with the axis of the aspherical surface.
However, such a lens cannot be really manufactured. In reality, a shift called eccentricity is slightly caused between the lens optical axis and the aspherical surface axis. Accordingly, when the aspherical lens is manufactured, it is necessary to measure eccentricity of this aspherical lens.
Some apparatuses for measuring eccentricity of the aspherical lens are generally proposed on the basis of such requirements.
In a measuring apparatus shown in Japanese Patent Application Laying Open (KOKAI) No. 3-37544, a detected lens as an aspherical lens is attached to a lens holder. A laser beam is irradiated onto the detected lens in a rotating axis direction thereof by approximately rotating the detected lens around an optical axis thereof. Thus, while a reflected spot image from the detected lens is monitored, the detected lens is moved in a direction perpendicular to the rotating axis thereof. A setting shift of the detected lens is corrected such that the rotating and optical axes of the detected lens are in conformity with each other. Thereafter, eccentricity of the detected lens is measured.
In addition to this measuring apparatus, various kinds of eccentricity measuring apparatuses are also proposed. However, in each of these eccentricity measuring apparatuses, the setting shift must be corrected such that the rotating and optical axes of the detected lens are in conformity with each other. Further, a high accuracy of about 1 .mu.m is required in this correction to secure a measuring accuracy in eccentricity.
Accordingly, skill is required for an operation for correcting the setting shift of the detected lens and it takes much time to perform this correcting operation.